title: Importance of trivalency and the e(g)(1) configuration in the photocatalytic oxidation of water by Mn and Co oxides.
abstract: Prompted by the early results on the catalytic activity of LiMn2O4 and related oxides in the photochemical oxidation of water, our detailed study of several manganese oxides has shown that trivalency of Mn is an important factor in determining the catalytic activity. Thus, Mn2O3, LaMnO3, and MgMn2O4 are found to be very good catalysts with turnover frequencies of 5 × 10(-4) s(-1), 4.8 × 10(-4) s(-1), and 0.8 × 10(-4) s(-1), respectively. Among the cobalt oxides, Li2Co2O4 and LaCoO3--especially the latter--exhibit excellent catalytic activity, with the turnover frequencies being 9 × 10(-4) s(-1) and 1.4 × 10(-3) s(-1), respectively. The common feature among the catalytic Mn and Co oxides is not only that Mn and Co are in the trivalent state, but Co(3+) in the Co oxides is in the intermediate t2g(5)e(g)(1) state whereas Mn(3+) is in the t2g(3e(g)(1) state. The presence of the e(g)(1) electron in these Mn and Co oxides is considered to play a crucial role in the photocatalytic properties of the oxides.
authors.affiliation: International Centre for Materials Science, Chemistry and Physics of Materials Unit, Sheik Saqr Laboratory and Council for Scientific and Industrial Research Centre of Excellence in Chemistry, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560 064, India.
authors.forename: Urmimala
authors.initials: U
authors.lastname: Maitra
authors.forename: B S
authors.initials: BS
authors.lastname: Naidu
authors.forename: A
authors.initials: A
authors.lastname: Govindaraj
authors.forename: C N R
authors.initials: CN
authors.lastname: Rao
mesh_terms: D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D004583:Electrons; D017895:Manganese Compounds / Q000737:chemistry*; D008968:Molecular Conformation; D053758:Nanoparticles / Q000737:chemistry; D010087:Oxides / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D010777:Photochemistry / Q000379:methods*; D010788:Photosynthesis; D012993:Solar Energy; D014867:Water / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D017895:Manganese Compounds; D010087:Oxides; D014867:Water; D003035:Cobalt; C027424:manganese oxide; D010100:Oxygen; C060728:cobalt oxide
keywords: artificial photosynthesis; water oxidation